Which two statements are true about the Global Enqueue Service, Instance Locks, and global enqueues in Oracle 12c RAC?

Correct is “E” and “F”!

“A” and “C” is wrong!

If ASM is clustered, additional processes related to cluster management will be running in the ASM instance. Some of these processes include the following:
. LMON: The global enqueue service monitor process
. LZ4Dn: The global enqueue service daemons
. LMSn The global cache service processes
. LCKn The lock processes

“B” and “D” is wrong!

Need for Global Concurrency Control
Oracle requires concurrency control because it is a multi-user system.
• Single-instance Oracle provides concurrency control:
— Latches or mutexes for memory structures
— Enqueues for resource control
— Buffer cache pins for cache management
• In RAC, structures and resources may be accessed by or modified by a session running on any database instance.
• RAC, therefore, requires additional global concurrency controls to mediate access across instances.
— Global locks control library and row cache access.
— Global enqueues control resource access.
— Cache fusion controls buffer cache access.

Latches and mutexes may only protect access to memory structures if they are accessed by processes in the same instance.
In RAC, latches and mutexes are still used, but for global concurrency control, some additional global enqueues are used to provide protection across instances.

“E” and “F” is right!

Global enqueues are used to control access to resources, where the owner(s), waiter(s) if any, or converter(s) if any, or both, may be sessions in the same or different instances. Some global enqueues serve the same purpose they would serve in a single instance. For example, table manipulation (TM) enqueues. transaction enqueues (TX), control file enqueues (cF), high watermark enqueues (Hw), sequence cache replenishment (sQ), and redo thread enqueues (RT) all serve the same purpose as they would in a single instance. However, there are master and shadow metadata structures as described earlier in this lesson in the GRD, and the mastering instance will keep track of the waiters and converters.
Instance locks are enqueues that represent resources in the row cache or library cache protected within each instance by pins, mutexes, or latches. For cross-instance concurrency control, an enqueue is used, the owner(s) of which is or are the instance(s) that is or are currently the “source of truth” with regard to the current state of that resource. The LCKO process acts as the owner, waiter, or converter of the enqueue as a “proxy” process representing the instance. These enqueues are known as instance locks.